[2.2.12] /etc/resolv.conf is removed if create a VM base on an specialized image

[yuxisun1217]

Hi,

In WALA-2.2.12, when I create a VM base on a specialized image, the /etc/resolv.conf file is removed and cannot be generated only if I restart network or reboot.

Reproduce steps:

1. Capture a running VM as a specialized image.
2. Create a VM base on this image.
3. Check /etc/resolv.conf

/var/log/messages:

Jun  8 13:25:26 wala74fips python: 2017/06/08 13:25:26.019325 WARNING VM is provisioned, but the VM unique identifier has changed -- clearing cached state
Jun  8 13:25:26 wala74fips python: WARNING! Cached DHCP leases will be deleted.
Jun  8 13:25:26 wala74fips python: WARNING! /etc/resolv.conf will be deleted.

Additional Info:

1. Root cause is when creating a VM and the /var/lib/waagent/provisioned file exists, wala runs "deprovision_handler.run_changed_unique_id()", it calls "del_resolv"(Line#212 in pa/deprovision/default.py), which will delete the /etc/resolv.conf.
   In my opinion, when we create a new VM, the /etc/resolv.conf will be regenerated by dhclient script or NetworkManager. Do we need to remove it? And if we have to remove it, I think we'd better restart network to regenerate it.

2. The WARNING logs "WARNING! Cached DHCP leases will be deleted.", "WARNING! /etc/resolv.conf will be deleted." are only printed in /var/log/messages but not in /var/log/waagent.log. I think we'd better also print them in /var/log/waagent.log.

• For RHEL-6 OS, these WARNING messages cannot be written into /var/log/messages. (All the "print" messages cannot be caught.)

Thanks!

[brendandixon]

@yuxisun1217 When the VM unique identifier changes, the VHD / image could be running anywhere, even in an entirely new region. If so, cached network state is almost certain to be invalid.

I don't believe the agent should "restart" the network in this case. That feels like distribution-related code that best belongs in a systemd unit.

However, we can make the changes necessary to ensure all messages get properly emitted to the log file.

[yuxisun1217]

Hi @brendandixon ,

Everytime the VM is booted, the NetworkManager(RHEL-7) or dhclient(RHEL-6) will regenerate the /etc/resolv.conf. When we create a VM base on the specialized image, the /etc/resolv.conf is a new file, not the cached one.
Besides, the dhclient(or NetworkManager) starts and then WALA removes the /etc/resolv.conf, so that if WALA remove /etc/resolv.conf, no one will regenerate it.
So I think wala doesn't have to removed the /etc/resolv.conf file.

[brendandixon]

@yuxisun1217 I appreciate the details. I need to consider distributions other than Red Hat as well.

[brendandixon]

Addressed by #776

[yuxisun1217]

Hi @brendandixon ,

In WALA-2.2.14, it seem that the 2nd issue still exists:
The "WARNING! Cached DHCP leases will be deleted." is only printed in /var/log/messages but not in /var/log/waagent.log.
Could you please help to confirm if it will be fixed? Thank you very much!

[brendandixon]

@yuxisun1217 That is correct. I have mixed emotions about writing the message to /var/log/waagent.log. The new code path is something of a special case. If you feel strongly about it, please open a new issue to suggest the code writes the messages to log file as well.

[yuxisun1217]

@brendandixon OK, got it. Thanks!